images: fix Archs expansion in makefile

[cpanato]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When we start the new build for kube-cross image we got this error

docker manifest create --amend gcr.io/k8s-staging-build-image/kube-cross:v1.15.7-canary-1 gcr.io/k8s-staging-build-image/kube-cross-amd64:v1.15.7-canary-1
Created manifest list gcr.io/k8s-staging-build-image/kube-cross:v1.15.7-canary-1
manifest for image gcr.io/k8s-staging-build-image/kube-cross-arm64:v1.15.7-canary-1 does not exist in gcr.io/k8s-staging-build-image/kube-cross:v1.15.7-canary-1
manifest for image gcr.io/k8s-staging-build-image/kube-cross-ppc64le:v1.15.7-canary-1 does not exist in gcr.io/k8s-staging-build-image/kube-cross:v1.15.7-canary-1
make: *** [/workspace/images/build/cross/../../Makefile.common-image:60: manifest] Error 1
ERROR

which looks like when we run the docker manifest create --amend we need to add all the images for the archs we built.

This piece of the make file https://github.com/kubernetes/release/blob/master/images/Makefile.common-image#L59 add the images to the command, but now we have more platforms and the command subst just replace one entry and not all entries in the PLATFORMS variable

for kube-cross we used to have just one platform and that works fine, but now we introduce more (can see in this PR: https://github.com/kubernetes/release/pull/1853/files) and the command broke.

this PR fix this issue by parsing the PLATFORMS and removing the linux/ from the PLATFORMS variable.

before:

docker manifest create --amend gcr.io/k8s-staging-build-image/kube-cross:v1.15.7-canary-1 gcr.io/k8s-staging-build-image/kube-cross-amd64:v1.15.7-canary-1

after the fix:

docker manifest create --amend gcr.io/k8s-staging-build-image/kube-cross:v1.15.7-canary-1 gcr.io/k8s-staging-build-image/kube-cross-amd64:v1.15.7-canary-1 gcr.io/k8s-staging-build-image/kube-cross-arm64:v1.15.7-canary-1 gcr.io/k8s-staging-build-image/kube-cross-ppc64le:v1.15.7-canary-1

/assign @justaugustus @saschagrunert @hasheddan @ameukam

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

Does this PR introduce a user-facing change?

images: fix Archs expansion in makefile

[cpanato]

/priority important-soon

[ameukam]

/lgtm

[cpanato]

/hold for more eyes

[hasheddan]

This looks reasonable to me, thanks @cpanato 👍

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ameukam, cpanato, hasheddan

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• images/OWNERS [cpanato,hasheddan]

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[cpanato]

will lift the hold since got a review from a sig-release TL 🚀

/hold cancel

will observe the kube-cross job